As an example of an optical redundant switching method in the past in an optical network system, for example, there is a technology disclosed in Patent Document 1 described below. An optical redundant switching apparatus disclosed in Patent Document 1 includes an optical coupler that divides signals of n channels received from an external apparatus to two directions for operating system signals and signals transmitted in the direction of an optical switch, respectively, and the optical switch that selects the signals in the direction of the optical switch divided by the optical coupler and outputs the signals as standby system signals. The optical redundant switching apparatus transmits the operating system signals to an operating system optical terminal station apparatus. The standby system signals selected by the optical switch are output to a standby system optical terminal station apparatus.
The operating system optical terminal station apparatus converts the input operating system signals into wavelengths λ1 to λn, which are different for each of channels, and outputs the operating system signals to a wavelength multiplexing apparatus. The standby system optical terminal station apparatus converts the standby system signals into a wavelength λ(n+1) and outputs the standby system signals to the wavelength multiplexing apparatus. The wavelength multiplexing apparatus multiplexes the wavelengths λ1 to λ(n+1) and transmits a wavelength-multiplexed signal to a wavelength multiplexing apparatus on a reception side opposed thereto. The wavelength multiplexing apparatus on the reception side separates the wavelength-multiplexed signal into the wavelengths λ1 to λ(n+1) and outputs, for each of the wavelengths λ1 to λ(n+1), the wavelength-multiplexed signal to an operating system optical terminal station apparatus and a standby system optical terminal station apparatus on the reception side. The operating system optical terminal station apparatus and the standby system optical terminal station apparatus on the reception side convert the wavelengths λ1 to λ(n+1) into operating system signals and standby system signals for each of the channels in a manner opposite to the that during the transmission and output the operating system signals and the standby system signals to an optical redundant switching apparatus on the reception side. When the signals of the channels are normal, the optical redundant switching apparatus outputs the operating system signals to an external apparatus by performing processing in a direction opposite to that during the transmission and discards the standby system signals.
In this optical redundant switching system, at the ordinary time, the transmission and reception of the operating system signals is performed between the external apparatus on the transmission side and the external apparatus on the reception side according to the procedure explained above. For example, when some failure occurs in an optical transmission line corresponding to λ2, an optical switch of the optical redundant switching apparatus on the transmission side selects an operating system signal of a second channel transmitted as λ2 after conversion and outputs the operating system signal as a standby system signal. The standby system signal is input to the optical redundant switching apparatus on the reception side through the standby system optical terminal station apparatus and the wavelength multiplexing apparatus and through the wavelength multiplexing apparatus and the standby system optical terminal station apparatus on the reception side opposed thereto. An optical switch of the optical redundant switching apparatus on the reception side selects this standby system signal to correspond to the operating system signal output of the second channel and outputs the standby system signal to the external apparatus.
In this way, in the example in the past, an n:1 optical redundant switching system is configured by adopting a method of remedying, when a failure occurs in any one of apparatuses or optical transmission lines corresponding to the signals of the n channels, an optical signal by switching to transfer a signal corresponding the transmission line, in which the failure occurs, via the standby wavelength (λ(n+1)) of the standby system.                Patent Document 1: Japanese Patent Application Laid-Open No. 2000-332655        